1. Field of the Invention
The present invention relates to a fabrication method of a nitride-based semiconductor device, particularly a fabrication method of a nitride-based semiconductor device, removing a support substrate on which a nitride-based semiconductor layer is formed after bonding between the nitride-based semiconductor layer and a retention substrate.
2. Description of the Background Art
A nitride-based semiconductor device typically employs a nitride-based compound semiconductor for the major portion of the device structure. Various devices such as a light emitting device, a light receiving device and a power device can be enumerated. In the case of a light emitting device such as an LED (Light Emitting Diode) or LD (Laser Diode), light emission corresponding to the wavelength range from ultraviolet to infrared can be obtained by appropriately selecting the composition of the nitride-based compound semiconductor employed in the light emitting layer.
A nitride-based compound semiconductor is, for example, a group III nitride determined by the compositional formula of AlaInbGa1−a−bN (0≦a≦1, 0≦b≦1, 0≦a+b≦1). Specific examples such as GaN, InGaN, AlGaN, AlInGaN, AIN, InN and the like, having an arbitrary composition, can be enumerated.
In the fabrication of a nitride-based semiconductor device, a semiconductor wafer is taken as the chip. The formation of a device structure includes the steps of depositing a nitride-based semiconductor layer on a support substrate that is a sapphire substrate or the like, and forming a P type ohmic electrode and an N type ohmic electrode on the nitride-based semiconductor layer to obtain a device (chip). However, this device structure is disadvantageous in that the electrodes occupy a relatively large area since two electrodes are formed on the nitride-based semiconductor layer, leading to the problem that the number of chips formed from one wafer is low.
In order to form many chips from one wafer, one conventional approach is to separate the wafer, after formation of a semiconductor layer thereon, from the semiconductor layer, and use the wafer again (Japanese Patent Laying-Open No. 2000-252224). FIG. 3 is a schematic sectional view to describe a conventional fabrication method of a nitride-based semiconductor device. Referring to FIG. 3, the conventional fabrication method includes the steps of depositing a stacked structure 27 constituted of a nitride-based semiconductor on a support substrate 2, bonding or attaching stacked structure 27 to a retention substrate 21 using a bonding metal 23, and working on the nitride-based semiconductor and retention substrate to produce a nitride-based semiconductor device.
The inventor of the present invention found, through evaluation experiments, that the conventional bonding method (the attaching method) had problems set forth below. When a support substrate with a stacked structure constituted of a nitride-based semiconductor is bonded to a retention substrate (attached together), followed by removal of the support substrate, cracking, fracture, chipping, and the like will occur at the retention substrate during removal of the support substrate. It is considered that placing a pair of forceps or the like during removal of the support substrate will cause cracking, fracture, chipping and the like at the retention substrate due to its weak strength.